I am repeating an EFA using the same data and the same Mplus code, but in different Mplus versions. The output were identical, except some factors had its factor loadings sign flipped(absolute values didn't change). What caused this change in the sign? Would this be a problem for using the EFA analysis result? Please help. Thanks!

If all of the signs in a column change, this is not a problem. There was probably a slight algorithm change between Version 5 and 5.21. It just changes the factor meaning from, for example, inability to ability.

I'm doing a single-dimensional factor analysis of categorical items where I'd like to obtain flipped loadings. I tried to fix the loading of the first indicator to -1 rather than 1, but wasn't able to deduce the correct syntax for this.